The ASM3P2879A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all digital method.
The ASM3P2879A modulates the output of a single PLL
in order to “spread” the bandwidth of a synthesized clock,
and more importantly, decreases the peak amplitudes of
its harmonics. This results in significantly lower system
EMI compared to the typical narrow band signal produced
by oscillators and most frequency generators. Lowering
EMI by increasing a signal’s bandwidth is called ‘spread
spectrum clock generation’.
Applications
The ASM3P2879A is targeted towards all portable
devices with very low power requirements like MP3
players, Notebooks and digital still cameras.
Product Description
The ASM3P2879A is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of clock frequencies. The ASM3P2879A reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of
all clock
dependent signals. The ASM3P2879A allows significant
system cost savings by reducing the number of circuit
board layers ferrite beads, shielding that are traditionally
required to pass EMI regulations.
Key Specifications
Description
Supply voltages
Cycle-to-Cycle Jitter
Output Duty Cycle
Modulation Rate Equation
Frequency Deviation
Specification
VDD = 2.5V / 3.3V
200pS (Max)
45/55%
F
IN
/640
±1% @ 24MHz
Block Diagram
VDD
XIN
Crystal
Oscillator
Frequency
Divider
Feedback
Divider
Modulation
PLL
XOUT
Phase
Detector
Loop
Filter
VCO
Output
Divider
ModOUT
REFOUT
VSS
Alliance Semiconductor
2575 Augustine Drive
•
Santa Clara, CA
•
Tel: 408.855.4900
•
Fax: 408.855.4999
•
www.alsc.com
Notice: The information in this document is subject to change without notice.
September 2005
rev 1.4
Pin Configuration (6-pin TSOT-23 Package)
ASM3P2879A
REFOUT
XOUT
1
2
6
VSS
ModOUT
VDD
ASM3P2879A
5
4
XIN/CLKIN
3
Pin#
1
2
3
4
5
6
Pin Name
REFOUT
XOUT
XIN/CLKIN
VDD
ModOUT
VSS
Type
O
O
I
P
O
P
Description
Buffered output of the input frequency.
Crystal connection. If using an external reference, this pin must be left unconnected.
Crystal connection or external reference frequency input. This pin has dual functions. It
can be connected either to an external crystal or an external reference clock.
Power supply for the entire chip (3.3V)
Spread spectrum clock output.
Ground connection.
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
2 of 12
September 2005
rev 1.4
Pin Configuration (8-pin SOIC and TSSOP Packages)
XIN/CLKIN
XOUT
1
2
8
VDD
7
6
ASM3P2879A
ASM3P2879A
NC
ModOUT
REFOUT
3
NC
4
5
VSS
Pin Description
Pin#
1
2
3
4
5
6
7
8
Pin Name
XIN/CLKIN
XOUT
REFOUT
NC
VSS
ModOUT
NC
VDD
Type
I
O
O
-
P
O
-
P
Description
Crystal connection or external reference frequency input. This pin has dual functions. It
can be connected either to an external crystal or an external reference clock.
Crystal connection. If using an external reference, this pin must be left unconnected.
Buffered output of the input frequency.
No connect.
Ground connection.
Spread spectrum clock output.
No connect.
Power supply for the entire chip
Modulation Profile
Specifications
Description
Frequency Range
For 2.5V Supply
For 3.3V Supply
Modulation Equation
Frequency Deviation
Specification
13MHz < CLKIN < 30MHz
13MHz < CLKIN < 30MHz
F
IN
/640
±1% @ 24MHz
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
3 of 12
September 2005
rev 1.4
Absolute Maximum Ratings
Symbol
VDD, V
IN
T
STG
T
A
T
s
T
J
T
DV
Storage temperature
Operating temperature
Max. Soldering Temperature (10 sec)
Junction Temperature
Static Discharge Voltage
(As per JEDEC STD22- A114-B)
ASM3P2879A
Parameter
Rating
-0.5 to +7.0
-65 to +125
0 to 70
260
150
2
Unit
V
°C
°C
°C
°C
KV
Voltage on any pin with respect to Ground
Note: These are stress ratings only and are not implied for functional use. Exposure to absolute maximum ratings for prolonged periods of time may affect
device reliability.
DC Electrical Characteristics for 2.5V Supply
(Test condition: All parameters are measured at room temperature (+25°C) unless otherwise stated)
Symbol
V
IL
V
IH
I
IL
I
IH
I
XOL
I
XOH
V
OL
V
OH
I
DD
I
CC
VDD
t
ON
Z
OUT
Input low voltage
Input high voltage
Input low current
Input high current
Parameter
Min
VSS - 0.3
2.0
-
-
-
-
-
1.8
-
-
2.375
-
-
Typ
-
-
-
-
3
3
-
-
1.2
3.5
2.5
-
50
Max
0.8
VDD + 0.3
-35
35
-
-
0.6
-
-
-
2.625
5
-
Unit
V
V
µA
µA
mA
mA
V
V
mA
mA
V
mS
Ω
XOUT output low current (@0.5V, VDD=2.5V)
XOUT output high current (@1.8V, VDD=2.5V)
Output low voltage (VDD = 2.5 V, I
OL
= 8mA)
Output high voltage (VDD = 2.5 V, I
OH
= 8mA)
Static supply current *
Dynamic supply current (2.5V, 24MHz and with no load)
Operating Voltage
Power-up time (first locked cycle after power-up)
Output impedance
* XIN/CLKIN pin is pulled low
AC Electrical Characteristics for 2.5V Supply
Symbol
CLKIN
ModOUT
f
d
t
LH
*
t
HL
*
t
JC
t
D
Input frequency
Output frequency
Frequency Deviation
Input Frequency = 13MHz
Input Frequency = 30MHz
Parameter
Min
13
13
-
-
0.8
0.5
-
45
Typ
-
-
±1.75
±0.80
1.7
0.9
-
50
Max
30
30
-
-
1.9
1.2
200
55
Unit
MHz
MHz
%
nS
nS
pS
%
Output rise time (measured from 0.7V to 1.7V)
Output fall time (measured from 1.7V to 0.7V)
Jitter (cycle to cycle)
Output duty cycle
* t
LH
and t
HL
are measured into a capacitive load of 15pF
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
4 of 12
September 2005
rev 1.4
DC Electrical Characteristics for 3.3V Supply
(Test condition: All parameters are measured at room temperature (+ 25°C) unless otherwise stated)
ASM3P2879A
Symbol
V
IL
V
IH
I
IL
I
IH
I
XOL
I
XOH
V
OL
V
OH
I
DD
I
CC
VDD
t
ON
Z
OUT
Input low voltage
Input high voltage
Input low current
Input high current
Parameter
Min
VSS - 0.3
2.0
-
-
-
-
-
2.5
-
-
2.7
-
-
Typ
-
-
-
-
3
3
-
-
1.2
4.5
3.3
-
45
Max
0.8
VDD + 0.3
-35
35
-
-
0.4
-
-
-
3.6
5
-
Unit
V
V
µA
µA
mA
mA
V
V
mA
mA
V
mS
Ω
XOUT output low current (@0.4V, VDD=3.3V)
XOUT output high current (@2.5V, VDD=3.3V)
Output low voltage (VDD = 3.3 V, I
OL
= 8mA)
Output high voltage (VDD = 3.3 V, I
OH
= 8mA)
Static supply current *
Dynamic supply current (3.3V, 24MHz and with no load)
Operating Voltage
Power-up time (first locked cycle after power-up)
Clock output impedance
* XIN/CLKIN pin is pulled low
AC Electrical Characteristics for 3.3V Supply
Symbol
CLKIN
ModOUT
f
d
t
LH
*
t
HL
*
t
JC
t
D
Input frequency
Output frequency
Frequency Deviation
Input Frequency = 13MHz
Input Frequency = 30MHz
Parameter
Min
13
13
-
-
0.6
0.4
-
45
Typ
-
-
±1.75
±0.80
1.6
1.0
-
50
Max
30
30
-
-
1.8
1.2
200
55
Unit
MHz
MHz
%
nS
nS
pS
%
Output rise time (measured from 0.8 to 2.0V)
Output fall time (measured at 2.0V to 0.8V)
Jitter (cycle to cycle)
Output duty cycle
*t
LH
and t
HL
are measured into a capacitive load of 15pF
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
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